Chain Dynamics Heterogeneity in Plasticized Poly(vinyl butyral) (PVB) as Elucidated by Solid-State NMR

The chain dynamics heterogeneity of the poly(vinyl butyral) (PVB) plasticized by triethylene glycol bis(2-ethylhexanoate) (TEG-EH) was investigated by various solid-state NMR techniques. The plasticized PVB shows two domains in distinct molecular dynamics differences, namely, rigid and soft domains, where the latter is the plasticizer-rich domain. The time domain low field NMR was first used to investigate the dynamics heterogeneity of the plasticized PVB, and the results show the decreasing activated energy of components in the soft domain of plasticized PVB (E-a=20.2 kJ/mol) as compared with that of the pristine one (E-a=24.3 kJ/mol). Detailed dynamics heterogeneity was obtained by high-field NMR with site-specific features. The quadrupole-echo H-2-NMR was adopted to elucidate the dynamics heterogeneity of the vinyl alcohol (VA) units, where only the hydroxyl group of VA is deuterated. The H-1-C-13 WISE NMR spectra show that there is not much difference in the mobility of the VB unit in PVB with and without plasticizer, whereas the glass transition temperature differed by approximately 53 & DEG;C. This is further supported by Torchia's T-1 relaxation measurements. The origin of such an unusual phenomenon is attributed to the critical role of the remaining VA (& SIM;22%) in the soft domain, where the VA units locally aggregate through hydrogen bonding. Also, the existence of a mobility gradient in the VB unit has been demonstrated. Moreover, the mobility difference for VB with different stereo-geometry (meso or racemic conformation) is observed for the first time. This indicates the importance of modulating the ratio of meso over racemic VB for controlling the macroscopic performance of PVB.

Automated summary

The chain dynamics heterogeneity of poly(vinyl butyral) (PVB) plasticized by triethylene glycol bis(2-ethylhexanoate) (TEG-EH) was investigated using solid-state NMR techniques. The plasticized PVB exhibited two domains with distinct molecular dynamics differences, referred to as rigid and soft domains, where the soft domain contained a higher concentration of plasticizer. The study revealed that the activation energy of components in the soft domain of plasticized PVB were lower compared to the pristine PVB.