Fluoride-responsive debond on demand adhesives: Manipulating polymer crystallinity and hydrogen bonding to optimise adhesion strength at low bonding temperatures
Fluoride-responsive debond on demand adhesives: Manipulating polymer crystallinity and hydrogen bonding to optimise adhesion strength at low bonding temperatures
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DOI：
10.1016/j.eurpolymj.2019.07.038
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发表时间：
2019-10-01
影响因子：
6
通讯作者：
Greenland, Barnaby W.
中科院分区：
文献类型：
--
作者：
Babra, Tahkur S.;Wood, Matthew;Greenland, Barnaby W.
本文报道了一系列六种氟响应性按需脱粘聚氨酯（PU）胶粘剂的无溶剂合成，其中含有甲硅烷基官能化的可降解单元（DU）。为了优化粘合剂的粘合强度和脱粘性质，PU的化学组成根据聚合物主链中多元醇或二异氰酸酯组分的结构而变化。用1H-1 NMR谱研究了聚合物在溶液中的解聚行为。结果表明，四丁基氟化铵（TBAF）引发DU单元的断裂，而不会不加选择地断裂多元醇主链。在暴露于氟离子时，PU经历解聚，如通过GPC分析所测量的，M-n减少64至90%。通过差示扫描量热法（DSC）、流变学和变温（VT）SAXS/WAXS分析表征PU的形态和热性能。每种技术都证明了超分子聚合物网络在热刺激下的可逆性。含聚丁二烯软链段的PU是无定形的，其玻璃化转变温度和粘弹性转变温度取决于软链段和二异氰酸酯起始材料的性质。含有聚酯软链段的PU表现出49 ℃的限定熔点。一系列PU的机械应力-应变分析表明，作为聚合物主链的化学响应降解的结果，在用TBAF处理30分钟后，每个PU都表现出大于70%的韧性降低。该材料采用酯基多元醇，在低至60摄氏度的粘合温度下表现出优异的粘合性。此外，这种材料可以热再粘合，如果破坏力没有损失的粘合强度超过三个脱粘-再粘合循环。搭接剪切粘合试验表明，暴露于氟离子时，粘合强度降低约40%（从11.4 MPa至7.3 MPa）。
This paper reports the solvent-free synthesis of a series of six fluoride responsive debond-on-demand polyurethane (PU) adhesives that contain a silyl functionalised degradable unit (DU). To optimise the adhesion strength and debonding nature of the adhesives, the chemical composition of the PUs was varied according to the structure of the polyol or the diisocyanate component in the polymer mainchain. H-1 NMR spectroscopy was used to study the depolymerisation behaviour in solution state. It showed that tetra-butylammonium fluoride (TBAF) triggered the breakdown of the DU unit without fragmenting the polyol mainchain indiscriminately. On exposure to fluoride ions, the PUs underwent depolymerisation with reductions in M-n ranging from 64 to 90% as measured by GPC analysis. The morphology and thermal properties of the PUs were characterised by differential scanning calorimetry (DSC), rheology and variable temperature (VT) SAXS/WAXS analysis. Each technique demonstrated the reversibility of the supramolecular polymer network under thermal stimuli. PUs containing poly(butadiene) soft segments were amorphous with glass transition and viscoelastic transition temperatures dependent on the nature of the soft segment and diisocyanate starting materials. The PU containing a polyester soft segment exhibited a defined melting point at 49 degrees C. Mechanical stress-strain analysis of the series of PUs showed each exhibited greater than 70% reduction in toughness after treatment with TBAF for 30 min as a consequence of the chemo-responsive degradation of the polymer mainchain. The material featuring an esterbased polyol demonstrated excellent adhesion at bonding temperatures as low as 60 degrees C. Moreover, this material could be thermally rebonded if broken by force without loss in adhesion strength over three debond-rebond cycles. Lap shear adhesion tests showed a reduction in adhesive strength of approximately 40% (from 11.4 MPa to 7.3 MPa) on exposure to fluoride ions.