Silane-terminated polyurethane applied to a moisture-curable pressure-sensitive adhesive using triethoxysilane

Abstract

A silane-terminated polyurethane (SPU) modified by a silane end-capper anilinomethyltriethoxysilane (AMTES) was synthesized and acted as a pressure-sensitive adhesive (PSA) which could be moisture-cured at room temperature without releasing CO₂. Tuning the NCO/OH ratio (R value) and polyols molecular weight altered the performances of the SPU, and satisfied different applications. Putting emphasis on the characteristic properties of PSA, the increase of R value enhanced the peel strength and holding power, but lowered the tack; increasing the polyols molecular weight reversed the trend of the peel strength, holding power and tack of PSA. The obtained PSA was thermostable at 250 °C and almost uncrystallized. Additionally, the glass transition temperature (T_g) and contact angle also changed with the R value and polyols molecular weight.

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1. Introduction

Having an excellent elastomeric performance, polyurethane (PU) has been used in a wide range of applications.^1,2 However, the conventional one-component PU cured in the air is accompanied with the unexpected generation of CO₂ which leads to the formation of bubbles within the PU materials, shadowing the performances.^3,4 This is due to the reaction between reactive NCO groups on the end of PU chains and water in the air.⁵ Therefore, a feasible method to avoid this problem is modifying PU by silane which can react with the NCO groups to obtain silane-terminated polyurethane (SPU) chains.^6,7 When end-capped by silane groups, the solidification of the SPU is moisture-curable in the air undergoing the processes of hydrolyzation and condensation reaction without releasing CO₂.^8–10 Additionally, PU modified by silane combines advantageous characteristics of PU and organosilicon. It overcomes the intrinsic poor low-temperature flexibility plus water resistance of PU and produces the excellent performance of organosilicon such as heat resistance in PU.^11–13

In previous studies, the synthesis of SPU involved with variety of silanes which could generally be classified into two types. One was those that can be used directly. Duan et al.¹⁴ used aminopropyltriethoxysilane (APTES) and tetramethoxysilane (TMOS) as end-capper to obtain urethane prepolymer and chain-extended polyurethane for reinforcement of silica aerogels. Hydroxyl-terminated poly(dimethylsiloxane) (PDMS) was attached to a polyurethane copolymer as a spacer.¹⁵ 3-Aminopropyl-triethoxysilane (γ-APS) and aniline-methyl-triethoxysilane (AMS) were used in Jiang's studies to investigate the effect of the end-capper and NCO/OH ration on the properties of polymer.^16,17 Another type of applied silane concerns a previous step of reaction to obtain end-capper. Nomura et al.^18,19 synthesized several end-cappers by the Michael addition reaction of commercially available 3-aminopropyltrimethoxysilane with acrylates to prepare one-component adhesive. Shaik et al.²⁰ synthesized a novel functional materials with 3-aminopropyltrimethoxysilane (APTMS) and 3-glycidoxypropyltrimethoxysilane (GPTMS) to prepare siloxane-crosslinked polyurethane urea/silica hybrid films. These examples presented that different silanes introduced in PU had different effects on the performances of the materials. Accordingly, we can choose appropriate silane end-capper to modify PU to satisfy various applications.

Pressure-sensitive adhesive (PSA) is a special class of adhesive that can stick two surfaces under an application of slight pressure.²¹ PSA was used widely in varying fields such as pressure-sensitive tapes, labels, note pads and automobile trim because of its simple processing and prominent stickness.²² Usually the PSA with excellent performances requires viscoelasticity, as PSA should be functionalized with high strength like solids and macroscopical mobility like liquids. Strong adhesion of PSA comes from the flowable molecular chains to wet surfaces and enough strength to stick two specimens.²³ It was pointed out in previous studies that two essential requirements for PSA with respect to structure were high cohesive energy and high molecular mobility.²⁴ Nevertheless, the coexistence of high cohesive energy and high molecular mobility of an adhesive polymer is a contradiction, as a higher cohesion among molecules is realized at the expenses of molecular mobility in most cases.²⁵ Consequently, a well-performed PSA is difficult to achieve.

As described before, due to the excellent performances of SPU, it has been applied in various fields such as coating, adhesive and sealant.^19,26 But the application of SPU in PSA was reported rarely. In this study, the SPU was served as PSA taking anilinomethyltriethoxysilane (AMTES) as silane end-capper on the basis of comprehensive considerations of various SPU mentioned in the previous studies. To satisfy the high cohesive energy and high mobility of PSA, which were mainly dominated by hard-segment content and soft-segment content respectively, we tuned the ratio of NCO/OH (R value) and molecular weight of polyols in the synthesis of SPU. We characterized the structures of the products generated the whole synthesis process. Our attention was focused on effects of different R value and polyols molecular weight on the characteristic properties for PSA which were consisted of peel strength, tack and holding power. We also investigated the thermal property, glass transition temperature (T_g), hydrophobicity and crystallization property depending on the R value and polyols molecular weight.

2. Experimental

2.1 Materials

Polypropylene glycol (PPG) (molecular weight of 1000, 2000, 3000 g mol⁻¹) was obtained from Shanghai Beike Chemical Engineering Co. Ltd (China). Diphenylmethane diisocyanate (MDI) was purchased from Yantai Wanhua Polyurethanes Co. Ltd (China). Anilino-methyl-triethoxysilane (AMTES) was obtained from Nangjing Youpu Chemistry Engineering Co. Ltd (China). All the chemicals were analytical grade and were used without further purification.

2.2 Synthesis of isocyanato-terminated PU prepolymer

PPG (M_n = 1000, 2000, 3000) was dewatered under vacuum at 120 °C for 2 h. The metric PPG and MDI were introduced into a three-neck flask equipped with a mechanical stirrer, a thermometer and a nitrogen inlet. The reaction was conducted under mechanical stirring at 80 °C for 5 h to get isocyanato-terminated PU prepolymer.

2.3 Synthesis of SPU prepolymer

The isocyanato-terminated PU generated at last step reacted with AMTES at a ratio of 1 : 1 for 2 h at 80 °C to get SPU prepolymer. Tuning R value and the PPG molecular weight, a suite of prepolymers were obtained with different formula. As the ratio of NCO groups and secondary amino groups of AMTES was 1 : 1, the isocyanato-terminated PU prepolymer was end-capped with silane-endcapper completely. The samples were named as SPUxxxx, as the first x represented the PPG molecular weight and the next three x signified the molar ratio of PPG : MDI : AMTES. For example, the sample SPU1122 was synthesized with PPG1000 and the molar ratio of 1 : 2 : 2 for PPG : MDI : AMTES. Table 1 lists various formulations of SPU with different R value and PPG molecular weight.

Table 1 Formulations of SPU with different R value and PPG molecular weight

Sample	PPG molecular weight (g mol^−1)	R value	Mass fraction of silane-endcapper (%)
SPU1122	1000	2	26.4
SPU1232	1000	1.5	16.3
SPU1342	1000	1.33	11.8
SPU2122	2000	2	17.7
SPU2232	2000	1.5	10.2
SPU2342	2000	1.33	7.1
SPU3122	3000	2	13.3
SPU3232	3000	1.5	7.4
SPU3342	3000	1.33	5.1

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2.4 Synthesis of cured SPU films

In order to characteristic the structure and properties of the SPUs obtained from these two steps, they were cast on PTFE plate to form films and moisture-cured for 3 d at room temperature in the air. Then the films were putted in vacuum drying oven for 2 h at 60 °C to obtain complete cured SPU films. The whole process of the synthesis of the cured SPU films is shown in Scheme 1.

Scheme 1 Preparation scheme of SPU films.

2.5 Characterizations

The viscous PU and SPU prepolymers were coated on the KBr disc via coating method. The chemical structure of films was studied by a Fourier transformation infrared spectrum (FTIR) (Nicolet is10, Thermo Scientific, USA) in the scanning range of 4000–400 cm⁻¹ for 32 times.

Dynamic thermomechanical analysis (DMA) was performed on a dynamic thermomechanical analyzer (Q800, Netzsch, GER) in stretch mode. The cured SPU films were clipped as a size of 15 mm × 4 mm × 0.2 mm, and dried for 5 h at 60 °C before test. These samples were scanned from −100 to 50 °C at a fixed frequency of 1 Hz and a amplitude of 20 μm, a heating rate of 3 °C min⁻¹.

The samples were dried in vacuum oven at 80 °C to a constant weight. Thermogravimetric analysis (TGA) was investigated by a thermogravimetric analyzer (TG209 F1, Netzsch, GER). The samples were scanned from 20 to 500 °C at a constant heating rate of 10 °C min⁻¹ in nitrogen atmosphere.

The chief properties of PSA contains 180° peel strength, tack and holding power. The SPU prepolymers were coated on polyester films evenly and moisture-cured for 3 d at room temperature. The samples with appropriate size were pasted to steel, PVC and glass plates and maintained for 2 h. 180° peel strength was measured on an electronic tensile testing machine (CMT4104, Shenzhen Xinsansi Material Co. Ltd, China). The 180° peel strength, tack and holding power were measured according to GB/T 2790-1995, GB/T 4852-84 and GB/T 4851-1998, respectively.

A contact angle measurement apparatus (DSA25, KRuSS, GER) was used to test the water contact angle of the cured SPU films. At a temperature of 25 °C and a water drop volume of 5 μL, every sample was measured at least for 5 times and calculated to obtain average values.

The cured SPU films were cut into slices at the size of 1 cm × 1 cm. X-ray diffraction (XRD) measurement was carried out on a XRD diffractometer (X′ Pert Pro MPD, Philips, NED) scanning from 3 to 60°.

3. Results and discussion

3.1 FT-IR analysis

Fig. 1 shows the IR spectroscopies of the specimens in the synthesis process of PSA consisting of (a), (b), (c) and (d), corresponding to silane-endcapper AMTES, isocyanato-terminated polyurethane, SPU and cured SPU, respectively. As shown in Fig. 1, characteristic absorption peak for NCO appears at 2274 cm⁻¹, which almost vanishes in (b) and completely vanishes in (c), manifesting a low content after end-capping and entirely reacting of NCO respectively. In the reaction of NCO end-capping, a complete reaction extent between secondary amino groups and NCO groups is hard to achieve at a molar ratio of 1 : 1 for the two groups. Thus there are a small amount of residual NCO groups in the SPU. But after curing surrounded by air, the residual NCO groups react slowly with moisture and then disappear completely. A new peak at 1678 cm⁻¹ appearing in (c) and (d), is attributable to the carbonyl stretching vibration of urea carbonyl generated from the reaction between NCO groups of PU and secondary amino groups of AMTES. Another peak of carbonyl stretching vibration locating at 1730 cm⁻¹ is assigned to urethane carbonyl. The curves (c) and (d) corresponding to the products before and after curing keep basically the same except the peak at 960 cm⁻¹. Certified by its appearances in (a), (c) and disappearance in (d), this peak can be attributed to Si–O–CH₂CH₃. Thus, from (c) to (d), the Si–O–CH₂CH₃ groups hydrolyzed and crosslinked to form Si–O–Si, resulting in the vanishment of the absorption peak at 960 cm⁻¹.

Fig. 1 The FT-IR spectra of specimens in the synthesis of PSA (a) AMTES (b) NCO-terminated PU (c) SPU (d) cured SPU.

3.2 DMA analysis

The effects of R values on the storage modulus and the tangent angles of SPU films are showed in curves (a) and (b) of Fig. 2. It can be clearly seen that three peaks at −2 °C, −15 °C, and −21 °C represent glass transition temperature of SPU1122, SPU1232, and SPU1342 respectively. Obviously, the significant increase in T_g of SPU films corresponds with an increase in R value, as can be concluded from a low proportion of soft/hard-segments in polyurethane, namely a low content of soft segments that causes difficulties for segment motion. This difficulties for segment motion resulted from a high R value can also be interpreted by a large number of crosslinking points and a high degree of crosslinking caused by a high NCO content and the increased silane end-capper introduced in the SPU. Based on these two points, the T_g of SPU films significantly increases with the increase of the R value.

Fig. 2 The effect of R value on storage modulus (a) and tan δ (b) of SPU films.

Fig. 3 shows the storage modulus and tangent angles of the SPU films prepared from different PPG molecular weight. It can be seen from Fig. 3(b) that the T_g of SPU films decreases with the increases of the PPG molecular weight at the fixed R value of 2. With respect to the segment motion ability, increasing the molecular weight of soft PPG could enhance the flexibility of the molecular chains and the easiness of the segment mobility, resulting in a lower T_g. Otherwise, at the same proportion in the system, increasing the PPG molecular weight means declining the silane end-capper content and the crosslinking points, causing a lower degree of crosslinking, which benefits the moving of molecular chains. Thus, the PPG molecular weight and R value can be tuned to adjust the T_g of PSA to satisfy different applications.

Fig. 3 The effect of PPG molecular weight on storage modulus (a) and tan δ (b) of SPU films.

As described previously, the adhesive properties of PSA are determined by the cohesive energy and the locomotivity of the polymer chains which are affected by the crosslinking and PPG molecular weight. Therefore, tuning the two factors can also influences the adhesive properties of PSA.

3.3 TGA analysis

Thermogravimetric analysis was applied to measure the thermal stability of materials. Fig. 4 and Table 2 shows the TGA curves and data of SPU films prepared from different R value and PPG molecular weight. As shown in Fig. 4, there are little differences for these TGA curves and a similar trend that all curves start declining above 200 °C. According to the Table 2, the initial degradation temperature is higher than 250 °C, and the R value shows a little effect to it. There is a temperature interval for chief degradation from 250 to 400 °C and two maximum degradation temperatures of the SPU films. A detailed analysis for the curves distinguished the temperature interval as two parts, 250–380 °C and 380–460 °C. At the first interval, hard-segments in the SPU films involving carbamate and allophanate segments degraded, while the soft-segments containing C–O–C, Si–O, Si–C degraded during the second interval. These conclusions are in accordance with the results demonstrated in previous reports.^27,28

Fig. 4 TGA curves of SPU with different R value and PPG molecular weight.

Table 2 The TGA data of SPU films

Sample	Initial decomposition temperature (°C)	Maximum decomposition temperature (°C)	Ultimate decomposition temperature (°C)	Remnant mass fraction (%)
SPU1122	256.1	315.1, 387.3	452.1	6.83
SPU1232	261.9	313.2, 387.0	451.0	6.03
SPU1342	277.4	319.2, 383.5	452.7	1.84
SPU2122	269.8	304.5, 386.2	423.6	6.38
SPU3122	274.1	309.0, 386.2	441.1	0.64

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Taking SPU1122, SPU1232, and SPU1342 for comparison, the mass loss fraction at the first interval increases with the increase of R value. It can be explained that the thermal degradation of hard-segments occurred at there. So a high R value implying a large content of hard-segment causes a high mass loss fraction. However, at the same trend of R value, the mass loss fraction presents an opposite change at the second temperature interval that corresponds to the degradation of soft-segments and crosslinking points. Based on the same mechanism, increasing the PPG molecular weight means increasing the soft-segment content, which would contribute to a fraction increase of mass loss at the second interval and a reverse trend at the first interval. This deduce is in agreement with the data of SPU1122, SPU2122 and SPU3122 from Table 1. According to Fig. 4 and Table 2, the prepared SPU films for PSA are endowed with a high thermostability and an initial thermal degradation temperature above 250 °C, and can be applied in general circumstances.

3.4 Adhesive properties of SPU films for PSA

The chief characteristic properties of PSA contain peel strength, tack and holding power. As the most important property for PSA, the peel strength is tuned variously for different application. So we focused lots of interests on the peel strength of PSA and investigated the tack and the holding power at the same times. Fig. 5–7 shows the peel strength of PSA depending on different PPG molecular weight and R value when adhered on steel, PVC and glass substrates respectively. As shown in Fig. 5, three curves with different PPG molecular weight of 1000, 2000 and 3000 exhibit the same trend that an increase in peel strength occurred with the enhancement of R value. This could be induced by the increased crosslinking points and crosslinking degree. As the enhanced R value results in the larger NCO content, causing the larger silane end-capper content which contribute to the generation of crosslinking. Hydrogen bonding among hard-segments and hydrolysis-crosslinking among siloxanes can reinforce the cohesive energy of PSA. Accordingly, an increased R value can enhance the peel strength of PSA due to the larger hard-segment content and the more crosslinking points. It also can be seen that the peel strength declines with the increases of the PPG molecular weight at the same R value, and its difference is more significant at the larger R value. Increasing the PPG molecular weight at the same R value, the proportion of soft-segments in the system decreases, causing the reducing of the hard-segments and crosslinking points. So the peel strength of PSA decreases. Fig. 6 and 7 illustrate a similar variation for peel strength with R value. It can be concluded that the peel strength of PSA increases with the increase of R value and the decrease of PPG molecular weight, as tested on substrates of steel, PVC and glass.

Fig. 5 The effect of R value on peel strength of SPU films with steel substrate.

Fig. 6 The effect of R value on peel strength of SPU films with PVC substrate.

Fig. 7 The effect of R value on peel strength of SPU films with glass substrate.

Besides the peel strength for PSA, investigation of tack and holding power are also essential. Tack is measured by the number of adhered steel ball, and holding power is expressed by the shedding time of the ball. Table 3 lists the peel strength, tack and holding power of PSA samples. As it shown, when the R value increases at the same PPG molecular weight, the peel strength increases and the tack enhances while the holding power declines. With the improvement of the PPG molecular weight at the same R value, a lower peel strength, a poorer holding power and a better tack are observed. Because tack is closely relevant to the soft-segment content, the higher it is in PSA, the lower T_g and the better tack PSA possesses. On the other hand, holding power and peel strength are connected with cohesive energy. Thus, increasing the amount of hard-segments, intermolecular hydrogen bonds and crosslinking structures is favourable for the enhancement of the peel strength and holding power of PSA.

Table 3 The adhesive property data of SPU to steel

Sample	Peel strength (N per 2.5 cm)	Tack	Holding power (h)
SPU1122	8.61	0	>24
SPU1232	7.17	3	>24
SPU1342	4.33	3	18
SPU2122	6.63	8	22
SPU2232	5.30	10	18
SPU2342	3.60	10	15
SPU3122	2.07	9	8
SPU3232	1.52	11	6
SPU3342	1.03	12	2

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3.5 Contact angle analysis

The static water contact angle analysis was performed to test the wetting capability of water to SPU samples. The contact angle photos are presented in Fig. 8 and the relevant data are reported in Table 4. The hydrophobicity of SPU films is mainly dominated by the Si–O–Si crosslinking structures generated from the hydrolysis-crosslinking process of SPU. The non-polar Si–O–Si structure is incompatible with the polar O–H structure in water. As a consequence, its increase will enhance the surface hydrophobicity and increase the contact angle of the samples. In the silane end-capping process, due to their low surface energy the Si–O–Si structures tended to migrate towards surface of the polymer to diminish the interfacial energy between polymer surface and air. So the Si–O–Si structures assembled on polymer surface, resulting in the increase of water contact angle. Photos (a), (b), (c) of Fig. 8 show contact angles of 99.8°, 88.8°, 82.3°, which corresponding to SPU1122, SPU1232, SPU1342 respectively. Obviously, the contact angle declines with the increase of R value. It can be attributed to the increased Si–O–Si structures due to the high R value as described previously. These structures on surface of the samples enhance the hydrophobicity, and then increase the contact angle. As for the comparison of SPU1122, SPU2122, SPU3122, which corresponding to photos (a), (d), (e) of Fig. 8 respectively, the contact angles are 99.8°, 95.4°, 88.6° in turn. As the PPG molecular weight increases, the contact angle declines. At the same conditions, increasing the PPG molecular weight at the R value of 2 will decreases the content of silane end-capper, which will decreases the Si–O–Si structures. And then the surface hydrophobicity and the contact angle decrease.

Fig. 8 Photos of water contact angle measurement of SPU films (a) SPU1122 (b) SPU1232 (c) SPU1342 (d) SPU2122 (e) SPU3122.

Table 4 The data of water contact angle of SPU films

Sample	Contact angle (°)	Standard deviation
SPU1122	99.8	0.3
SPU1232	88.8	0.2
SPU1342	82.3	0.2
SPU2122	95.4	0.3
SPU3122	88.6	0.3

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3.6 X-ray diffraction analysis

Crystals within the SPU samples influence the cohesive energy of SPU molecule and further make an effect on the adhesion of PSA.²⁹ Fig. 9 shows the XRD curves of SPU1122 and SPU1232 to investigate the crystallizations. A broad dispersive peak at about 2θ = 20° for each of the samples is observed. It reveals that there is not significant crystallization within the SPU samples.³⁰ Taking PPG as the soft-segment component will restrict the formation of crystal of the SPU samples as its side-chain methyl on the molecular chain destroys its regularity. The hard-segments are composed of MDI whose structure is irregular. The introduced silane end-capper will further destroy the regularity of hard-segments and add more difficulties to the crystallization for hard-segments of SPU samples. As a result, there is no crystal for both soft-segments and hard-segments of the sample, which is illustrated on the XRD as a broad dispersive peak.

Fig. 9 XRD profile of SPU films.

4. Conclusion

The silane end-capper AMTES was introduced to the preparation of SPU that was synthesized by MDI and PPG and was served as PSA. Varying the NCO/OH ratio and PPG molecular weight, the variation of the SPU properties were investigated. With the increase of R value, the T_g of SPU decreased and the hydrophobicity increased. The same trend occurred at the situation of decreasing the PPG molecular weight. The obtained PSA was thermostable at 250 °C and almost uncrystallized. As for the characteristic properties of PSA, increasing the R value as well as decreasing PPG molecular weight enhanced the peel strength and holding power, but lowered the tack. The variation of R value and PPG molecular weight acted on the soft-segment and hard segment content, and then influenced the cohesive energy and chains mobility, further determined the adhesive properties of PSA. Consequently, diverse properties of PSA to satisfy different applications can be achieved by tuning the R value and PPG molecular weight.

Acknowledgements

The authors would like to thank the financial support from National Natural Science Funds for Distinguished Young Scholar (Grant No. 51603132).

References

1. G. Oertel, Polyurethane handbook, Hanser, New York, 1983.
2. C. Hepburn, Polyurethane elastomers, Applied Science, New York, 1982.
3. O. Kläusler, W. Bergmeier, A. Karbach, W. Meckel, E. Mayer, S. Clauß and P. Niemz, Int. J. Adhes. Adhes., 2014, 55, 69–76.
4. M. Sterley, S. Trey, A. Lundevall and S. Olsson, J. Appl. Polym. Sci., 2012, 126, 296–303.
5. D. Ren and C. E. Frazier, Int. J. Adhes. Adhes., 2013, 45, 118–124.
6. Z. Hea, Q. Li, J. Wang, N. Yin, S. Jiang and M. Kang, Constr. Build. Mater., 2016, 116, 110–120.
7. M. Zanetti, D. Marini, E. Pasqualini, E. Masetto and R. Cavalli, Eur. J. Wood Wood Prod., 2016, 74, 127–130.
8. H. Ni, W. J. Simonsick, A. D. Skaja, J. P. Williams and M. D. Soucek, Prog. Org. Coat., 2000, 38, 97–110.
9. H. Ni, A. D. Skaja and M. D. Soucek, Prog. Org. Coat., 2000, 40, 175–184.
10. Y. Nomura, S. Sato, H. Mori and T. Endo, J. Appl. Polym. Sci., 2008, 109, 608–616.
11. S. Sato and A. Sato, Jpn. Pat., 3 030 020, 2000.
12. S. Sato and A. Sato, Jpn. Pat., 3 317 353, 2002.
13. A. Inoue, S. Mori and S. Sato, Jpn. Pat., 3 471 667, 2003.
14. Y. Duan, S. C. Jana, B. Lama and M. P. Espe, Langmuir, 2013, 29, 6156–6165.
15. Y. Chung, N. D. Khiem and B. C. Chun, Polym. Eng. Sci., 2015, 55, 1931–1940.
16. H. Jiang, Z. Zheng, W. Song, Z. Li and X. Wang, Polym. Bull., 2007, 59, 53–63.
17. H. Jiang, Z. Zheng, W. Song and X. Wang, J. Appl. Polym. Sci., 2008, 108, 3644–3651.
18. Y. Nomura, A. Sato, S. Sato, H. Mori and T. Endo, J. Polym. Sci., Part A: Polym. Chem., 2007, 45, 2689–2704.
19. Y. Nomura, A. Sato, S. Sato, H. Mori and T. Endo, J. Appl. Polym. Sci., 2008, 108, 236–244.
20. A. Shaik, R. Narayan and K. V. Raju, J. Coat. Technol. Res., 2014, 11, 397–407.
21. C. Creton, MRS Bull., 2003, 28, 434–439.
22. I. Benedek and M. M. Feldstein, Handbook of Pressure-Sensitive Adhesives and Products, CRC press, Boca Raton, 2009.
23. D. W. Swanson, Adhesives Technology for Electronic Applications, Elsevier, Amsterdam, 2011.
24. M. M. Feldstein and R. A. Siegel, J. Polym. Sci., Part B: Polym. Phys., 2012, 50, 739–772.
25. M. M. Feldstein, E. E. Dormidontova and A. R. Khokhlov, Prog. Polym. Sci., 2015, 42, 79–153.
26. A. M. Mikhailova, M. Tamboura and M. Q. Jia, J. Coat. Technol. Res., 2013, 10, 97–108.
27. K. Pielichowshi and J. Njuguna, Thermal Degradation of Polymeric Materials, Rapra Technology, Shawbury, 2005.
28. F. Chuang, H. Tsia, J. Chow, W. Tsen, Y. Shu and S. Jang, Polym. Degrad. Stab., 2008, 93, 1753–17761.
29. S. Mondal and J. L. Hu, Polym. Eng. Sci., 2008, 48, 233–239.
30. T. Zhang, K. Xi, X. Yu, M. Gu, S. Guo, B. Gu and H. Wang, Polymer, 2003, 44, 2647–2654.

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