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We describe the POLAMI (Polarimetric Monitoring of AGN at Millimetre Wavelengths) programme for the monitoring of all four Stokes parameters of a sample of bright radio-loud active galactic nuclei with the IRAM30-m telescope at 3.5 and 1.3 mm. The programme started in 2006 October and accumulated, until 2014 August, 2300 observations at 3.5 mm, achieving a median time sampling interval of 22 d for the sample of 37 sources. This first paper explains the source selection, mostly blazars, the observing strategy and data calibration and gives the details of the instrumental polarization corrections. The sensitivity (1σ) reached at 3.5mm is 0.5 per cent (linear polarization degree), 4.°7 (polarization angle), and 0.23 per cent (circular polarization), while the corresponding values at 1.3mm are 1.7 per cent, 9.°9 and 0.72 per cent, respectively. The data quality is demonstrated by the time sequences of our calibrators Mars and Uranus. For the quasar 3C 286, widely used as a linear polarization calibrator, we give improved estimates of its linear polarization, and show for the first time occasional detections of its weak circular polarization, which suggests a small level of variability of the source at millimeter wavelengths. [ABSTRACT FROM AUTHOR]

The source NRAO?150 is a very prominent millimeter to radio emitting quasar at redshift z = 1.52 for which previous millimeter VLBI observations revealed a fast counterclockwise rotation of the innermost regions of the jet. Here we present new polarimetric multi-epoch VLBI-imaging observations of NRAO?150 performed at 8, 15, 22, 43, and 86?GHz with the Very Long Baseline Array (VLBA), and the Global Millimeter VLBI Array (GMVA) between 2006 and 2010. All new and previous observational evidence - i.e., spectral index maps, multi-epoch image cross-correlation, and low level of linear polarization degree in optically thin regions - are consistent with an interpretation of the source behavior where the jet is seen at an extremely small angle to the line of sight, and the high frequency emitting regions in NRAO?150 rotate at high speeds on the plane of the sky with respect to a reference point that does not need to be related to any particularly prominent jet feature. The observed polarization angle distribution at 22, 43, and 86?GHz during observing epochs with high polarization degree suggests that we have detected the toroidal component of the magnetic field threading the innermost jet plasma regions. This is also consistent with the lower degree of polarization detected at progressively poorer angular resolutions, where the integrated polarization intensity produced by the toroidal field is explained by polarization cancellation inside the observing beam. All this evidence is fully consistent with a kinematic scenario where the main kinematic and polarization properties of the 43?GHz emitting structure of NRAO?150 are explained by the internal rotation of such emission regions around the jet axis when the jet is seen almost face on. A simplified model developed to fit helical trajectories to the observed kinematics of the 43?GHz features fully supports this hypothesis. This explains the kinematics of the innermost regions of the jet in NRAO?150 in terms of internal jet rotation. [ABSTRACT FROM AUTHOR]