C-H…O Weak Hydrogen-Bonding Interaction In Polymer Blends Studied By SSNMR And FTIR Spectroscopies

Intermolecular interaction is a fundamental issue in polymer science.Hydrogen bonding is a common intermolecular interaction in polymer blends and the strong hydrogen-bonding interaction has been intensively studied.However,the study on weak hydrogen bonding in polymer blends is rare.Therefore,in this work,fourier transform infrared（FTIR）,solid-state nuclear magnetic resonance spectroscopy（SSNMR）and quantum calculation have been utilized to study the weak hydrogen-bonding interactions in three classical polymer blends,including the poly（methyl methacrylate）/polystyrene（PMMA/PS）blends,PS/poly（vinyl methyl ether）（PVME）blends and PMMA/poly（4-vinylphenol）（PVPh）blends.The details are as follows:1.The intermolecular interactions in PMMA/PS and PMMA^l/PS^l blends were first studied by SSNMR and quantum calculation.PMMA and PS with higher molecular weights were incompatible,in contrast to the miscibility of PMMA^l/PS^l blends with lower molecular weights.Correlation peaks between benzene rings of PS and C=O as well as OCH₃ groups of PMMA were detected by using 2D ¹³C-¹H Frequency Switched Lee-Goldburg heteronuclear correlation（FSLG-HETCOR）spectrum,showing the possibilities of the C-H…O bond between C=O and benzene rings,as well as the C-H…πor C-H…O bonds between OCH₃ and benzene rings.The identical local dynamics of OCH₃ groups studied by using 2D ¹³C{¹H}REREDOR sideband spectra revealed the existence of C-H…O rather than C-H…πbond between OCH₃ and benzene rings.Besides,quantum calculation showed that the distances between aromatic CH and C=O as well as OCH₃ oxygen were 2.724?and3.300?respectively,both shorter than the inter-chain distance of 3.873?between aromatic carbon and its para proton,verifying the existence of C-H…O weak hydrogen-bonding interactions between benzene rings and C=O as well as OCH₃ groups in PMMA^l/PS^l blends.2.FTIR,SSNMR and quantum calculation methods were utilized to study the C-H…O weak hydrogen-bonding interaction in PS/PVME blends.FTIR frequency-shifts of aromatic CH and C=C bands indicated that benzene rings were involved in the intermolecular interactions in PS/PVME.Moreover,correlation peak between OCH₃ and benzene rings was detected by using 2D ¹³C-¹H FSLG-HETCOR spectrum.¹³C longitudinal spin-lattice relaxation time（T₁）values showed that the local mobility of benzene rings was higher while that of OCH₃ group was lower after blending.According to the quantum calculation,the space distance between OCH₃ oxygen and aromatic CH was 2.524?,less than the inter-chain distance of 3.871?between aromatic carbon and its para proton.These findings all confirmed the existence of C-H…O weak hydrogen bonds between OCH₃ and aromatic rings in PS/PVME blends.3.The intermolecular interactions in PMMA/PVPh blends were studied by FTIR,SSNMR and quantum calculation methods.FTIR spectra showed the blue shift of aromatic C=C absorption,implying that benzene rings took part in certain intermolecular interaction in blends.The OCH₃ carbon peak was shifted to a higher frequency in ¹³C{¹H}cross polarization（CP）spectrum of blends.Meanwhile,correlation peaks between benzene rings and OCH₃ as well as C=O groups of PMMA were detected by using 2D ¹³C-¹H FSLG-HETCOR spectrum.The invariant local dynamics of OCH₃ groups from 2D ¹³C{¹H}REREDOR sideband spectra revealed the weak hydrogen-bonding interactions associated with the C-H…O rather than C-H…πbond between OCH₃ and benzene rings.Besides,quantum calculation of PMMA and PVPh showed that the distances between aromatic proton and C=O as well as OCH₃ oxygen were 2.939?and 3.522?respectively,both less than the inter-chain distance of 3.866?between aromatic carbon and its para proton.It confirmed the C-H…O weak hydrogen-bonding interactions between benzene rings and C=O as well as OCH₃ groups in PMMA/PVPh blends.In addition,the OH proton signals of PVPh were detected by 2D ¹³C-¹H FSLG-HETCOR technique,and identified based on the high resolution ¹H spectrum.